A. Technical Field
The present invention relates to a cement admixture and a cement composition, and more particularly, to a cement admixture and a cement composition, both of which have excellent fluid retainability of cement paste, mortar or concrete at high temperature and further display excellent fluidity even at low temperature.
B. Background Art
Since early deterioration of concrete structures became social problems in 1981, it has been strongly required to improve execution and durability of the concrete structures by decreasing the unit water quantity of concrete. Thus, a lot of technological innovation is carried out to a cement admixture which gives much influence to the quality and the capability of a cement mixture.
As to conventional methods, a fluidizing construction method is carried out, in which raw concrete of low fluidity (hereinafter, the fluidity is referred to as "slump") containing an air entraining (AE) agent or AE water-reducing agent is produced in a plant, and then transported to a building site with a raw concrete car, and then fluidized by adding a fluidizing agent, thereby raising the slump to a predetermined value. However, this construction method, for example, has the following problems: environmental problems due to noises and exhaust gases which are generated when adding the fluidizing agent to the concrete and then stirring and mixing them on the raw concrete car; problems of where the responsibility for the quality of the resultant fluidized concrete is assigned; and problems of great slump-decreasing with time of the fluidized concrete (hereinafter, the "slump-decreasing with time" is referred to as "slump loss").
Thus, a so-called high performance AE water-reducing agent which can be added in a raw concrete plant is energetically developed. However, it is the present condition that there are cases where the slump loss cannot sufficiently be suppressed under hard usage conditions such that the resultant raw concrete is transported to a remote place in summer.
On the other hand, in winter when the temperature is low, the water-reducibility deteriorates, and the required amount of the water-reducing agent added to obtain a predetermined fluidity therefore increases, so there are problems about the quality management of the concrete.